1. Field of the Invention
The present invention relates to a hydraulic shock absorber, which has an improved structure of a gas chamber defined by a partition wall member such as a free piston.
2. Description of the Related Art
For hydraulic shock absorbers used in four-wheeled vehicles and two-wheeled vehicles, there has been proposed an erect strut type structure as disclosed in Japanese Utility Model Application Laid-Open (JP-U) No. 51-129988, and an inverted strut type structure shown in FIG. 5. As shown in the prior art, FIG. 5, the hydraulic shock absorber 1 has a cylinder 2 is filled with a hydraulic fluid, and a piston 3 is slidably provided therein. The piston 3 is provided with a damping valve 4 for generating a damping force, and is connected to one end of a piston rod 5. Further, in order to absorb the capacity resulting from the piston rod 5 reciprocating in the cylinder 2, the cylinder 2 is formed with a gas chamber 6, and a free piston 8 partitioning the gas chamber 6 and an oil chamber 7 is slidably provided in the cylinder 2.
On the inner circumferential surface of the cylinder 2, in the slidable range Y of the free piston 8 is grease lubrication. In the slidable range X of the piston 3 is a hydraulic fluid lubrication (oil lubrication). Thus, in order to improve the responsibility of free piston 8 and a resistant abrasion performance of the free piston 8 and the cylinder 2, a surface roughness (coarseness) of the slidable range Y of the free piston 8 must be twice the degree as the surface roughness of the slidable range X of the piston 3. For this reason, there is a problem of increasing the number of processes for machining the cylinder 2.
Further, in the cylinder 2, the slidable range Y of the free piston 8 is set outside the slidable range X of the piston 3; for this reason, a stopper 9 for stopping a sliding motion of the free piston 8 must be fixed in the cylinder 2. This increases the number of processes for machining the cylinder 2.
Further, a gas is encapsulated in the cylinder 2, and thereafter, a hydraulic fluid is filled therein, and thus, the aforesaid hydraulic shock absorber 1 is assembled. For this reason, an assembling apparatus becomes complicate, and is made into a large size, and in addition, the number of processes for assembling the hydraulic shock absorber 1.
Moreover, in the aforesaid hydraulic shock absorber 1, a stud 2A for vehicle body attachment is fixed onto the cylinder 2 by bending the end portion of the cylinder 2. When a lateral direction (direction perpendicular to an axis of the hydraulic shock absorber) load (torsion (twisting) load F) is applied (acts) onto the stud 2A, an insertion length of the stud 2A with respect to the cylinder 2 is short. For this reason, there is a need of increasing a strength of bending the stud 2A to the end portion of the cylinder 2 in order to secure a strength against the torsion load F.